1. Field of the Invention
The present invention relates to a liquid-crystal polyester resin composition in which the largest defects of the liquid-crystal polyester, i.e. a large anisotropy (difference in properties between the machine direction of a resin and the direction transverse thereto in a molded product) and a low weld strength, have been improved.
2. Prior Art
The liquid-crystal polyester comprises rigid molecules unlike crystalline polyesters such as polyethylene terephthalate and polybutylene terephthalate, so that the molecules do not tangle with one another even in a molten state. Thus, the molecules form polydomains in a crystallized state, and the molecular chains markedly orient in the machine direction by a low shear. For this reason, the liquid-crystal polyester is generally called thermotropic liquid-crystal polymer or melt-type liquid-crystal polymer. Because of this peculiar behavior, this polyester has strong points that the melt flowability is very superior, a molded product having thin-wall portions of about 0.2 to about 0.5 mm in thickness can be easily obtained and besides this molded product has a high strength and a high stiffness. However, it has also defects that the anisotropy is very large and the weld strength is remarkably low.
In order to improve the foregoing defects of the liquid-crystal polyester, it is generally carried out to incorporate glass fibers into the polyester. It is known that when glass fibers are incorporated into the conventional crystalline polyesters, the glass fibers orient in the machine direction to develop anisotropy, but that when glass fibers are incorporated into the liquid-crystal polyester, the orientation of the molecular chains is disturbed by the glass fibers, so that the degree of anisotropy is reduced and also the weld strength is somewhat improved. Such the glass fiber-containing liquid-crystal polyester is mainly used in electronic parts such as coil bobbins, relay parts, connectors, etc. and contributes to miniaturizing the electronic parts and making the wall thereof thinner. However, even this method to incorporate glass fibers into the liquid-crystal polyester is not said to be satisfactory in an effect to improve the anisotropy and the weld strength. Therefore, when this method is applied to the production of the electronic parts, devices are necessary in determining the gate position, etc. Also, there have been problems in applying this method to the production of precision parts having a complicated form.
On the other hand, Japanese Patent Application Kokai No. 61-195156 discloses that when whiskers such as potassium titanate fibers are incorporated into a wholly aromatic polyester of a particular structure showing a thermotropic liquid crystalline property, anisotropy on mold shrinkage is more improved than when glass fibers are incorporated into the polyester. However, even suggestions are not given as to the improvement of the weld strength.